Inkjet recording methods are methods of printing by jetting ink droplets to make them adhere on a recording medium such as paper. As inks used in the inkjet recording methods, generally, a solution or dispersion liquid is used in which various colorants such as dyes and pigments are dissolved or dispersed in water or a mixture of water and a high-boiling point organic solvent, and to maintain moisture retention, a large amount of a wetting agent composed of a high-boiling point organic solvent is further contained therein. Such a wetting agent composed of a high-boiling point organic solvent contributes to prevention of drying of nozzle ports because of its low-volatility (evaporativity) and water-retention ability. When such an ink is used for recording on paper having high-ink permeation, for example, with regular paper, however, the wetting agent contained in the ink is hardly volatile, resulting in frequent ink strike through.
Meanwhile, when a conventional ink containing a large amount of wetting agent is used for recording on paper which has low liquid absorbability such as offset printing coated paper (hereinafter, may be referred to as “coated paper”), ink beading and ink bleeding are liable to occur in portions with a large amount of the ink, such as solid parts, due to its low-permeation rate of the ink provided on a surface of the coated paper thereinto, it takes some time to dry a recorded image because the wetting agent is hardly likely to evaporate, causing offset smear due to spurs, smear during conveyance, and paper stain and/or paper-sticking at paper stacked section in a paper-feed unit, etc. Thus, such a conventional ink is inappropriate in practical use.
In order to solve the problems, it has been desired to provide an inkjet recording method that allows ink bleeding to hardly occur even with the use of printing coated paper, allows ink to dry quickly, allows for high-image density and high-image quality even when an ink is printed on regular paper, and allows nozzle clogging to hardly occur even during long-time stoppage of printing operation.
For example, Patent Literature 1 proposes an inkjet ink containing an extremely small amount of a wetting agent. According to the proposal, it is possible to obtain high-quality image with high-image density without substantially causing ink strike through even when regular paper is used. However, in this proposal, no resin is contained in the ink, and particularly when a pigment ink is used, the fixing ability of image is poor. Further, improvements in drying rate of ink when the ink is printed on offset coated paper are not disclosed nor suggested in the proposal.
Patent Literature 2 proposes a quick-drying dye ink. In Examples of this proposal, however, the amount of a wetting agent is contained 6 times the amount of a colorant used with no addition of resin; high-quality paper is used, and printing coated paper, which extremely hardly absorbs liquid, is not intended for use.
Patent Literature 3 proposes a quick-drying ink relating to inkjet recording based on energization heat generation. However, the ink provided in this proposal contains a large amount of electrolyte with no addition of resin, the fixing ability of image is poor, and an ink-flying method is employed which is essentially different from piezo-type inkjet method.
Further, each of Patent Literature 4 and Patent Literature 5 proposes a combination of a micro-capsulated pigment and printing paper. However, in these proposals, the inks have generally used ink compositions. Thus, in order to improve the drying properties thereof, heating by microwave energy is required.
Patent Literature 6 proposes an ink containing wax fine particles and resin fine particles. In this proposal, the wax fine particles are used in place of a wetting agent, in terms of capability of imparting moisture retention. However, the wax fine particles having moisture retention tend to be poor in fixing property and dryness.
Patent Literature 7 proposes an ink containing a resin emulsion, a polymer dispersant and a pigment. The ink provided in this proposal contains a small amount of a wetting agent, but the total dissolved solid content is low. Therefore, sufficient image density and sufficient color-development may not be obtained.
Patent Literature 8 proposes as an ink suitable for non-porous recording media, such as film, an ink resin emulsion which contains an aqueous liquid vehicle with an acid function polymer colloid particle dispersed therein, and a pigment colorant in which polymer molecules are bonded to each other, and proposes an ink containing a polymer dispersant and a pigment. In the Examples of this proposal, a high-boiling point wetting agent (water-soluble organic solvent) is contained about 3.5 times the solid component, and in drying process of image recorded with the ink by leaving it under normal environments, it becomes necessary to heat and dry the ink by means of a heat gun due to its slow drying.
Further, Patent Literature 9 describes a pigment ink in order to simultaneously achieve two opposed objects of an object of preventing nozzle clogging and another object of quick drying of ink on a recording medium after recorded. In the pigment ink, the amount of glycerine contained (X), which is effective in to preventing nozzle clogging, and the amount of isopropanol contained (Y), used as a high-volatile solvent, which is effective in drying a recoded image, are specified within the ranges, 1≦X≦40, 1≦Y≦20, and 5≦X+Y≦50, respectively. This technique does not disclose a recording ink allowing for obtaining highly sharp images that are close in quality to recorded matters produced by commercial printing or printed matters for publication without substantially causing ink beading and without any problems with the drying rate of ink even when the ink is printed on printing coated paper which has low liquid absorbability, in view of adjustments of the ratio of three components of the colorant amount, the amount of solid contents and the amount of the water-soluble organic solvent having a high-boiling point of 280° C. or higher, besides additive amounts, and the contents. Patent Literature 10 discloses an inkjet ink in which a difference in weight ratio between nonvolatile components contained in a recording liquid (including resin and wax) and coloring material components falls in the range of from 0.1 to 10 at 25° C. for the purpose of improving the image density when printed on non-coated paper and improving abrasion resistance of printed matters. Patent Literature 11 discloses an ink containing as essential components a dye and a solvent for dissolving the dye and further containing a fluorochemical surfactant for exhibiting quick-drying properties by decreasing the surface tension of the ink so as to improve the wettability of the ink to a target recording medium and a large amount of an organic solvent for improving solubility of the fluorochemical surfactant in the ink, and described that the surface tension of the ink at 25° C. and the ink viscosity thereof at 20° C. are reduced to improve the frequency responsiveness of discharge ink by making uniform dispersibility of the components in the ink responsive to high-speed printing, thereby ejecting small droplets of ink. Patent Literature 12 describes an ink in which a pigment and a micro emulsion are contained in an aqueous medium, the micro emulsion has an average particle diameter of 50 nm or less, the amount of the micro emulsion contained is 0.5% by mass to 10% by mass based on the total mass of the ink, and with the use of the ink, the density of printed matters, when printed on non-coated paper, is increased, thereby improving abrasion resistance of the printed matters. However, these proposals do not disclose a technique allowing for obtaining highly sharp images that are close in quality to recorded matters produced by commercial printing or printed matters for publication without substantially causing ink beading and without any problems with the drying rate of ink even when printed on printing coated paper which has low liquid absorbability, in view of adjustments of the ratio of three components of the colorant amount, the 1.0 amount of solid contents and the amount of the water-soluble organic solvent having a high-boiling point of 280° C. or higher, besides additive amounts, and the contents.
Thus, it has not been intended to apply such conventional inkjet recording inks to recording media which have low-liquid absorbability, like printing coated paper such as offset printing coated paper, and in the conventional inkjet recording media, such a technique has not yet been developed that reduces the amount of a liquid component(s) (primarily, wetting agent) which has a boiling point higher than that of water and is liquid in ink, with focusing on the ratio with the amount of solid components in the ink to thereby improve the permeation property of the ink, and determines the amount of the liquid component(s) so as to fall in the range where troubles such as a change in the orbit of the ejected ink (ejection curve) and non-ejection of ink during printing or during short-time stoppage of printing operation, and nozzle clogging during long-time stoppage of printing operation can be avoided.
Patent Literature 1 Japanese Patent Application Laid-Open (JP-A) No. 2004-115551
Patent Literature 2 Japanese Patent Application Publication (JP-B) No. 60-34992
Patent Literature 3 Japanese Patent Application Laid-Open (JP-A) No. 8-109343
Patent Literature 4 Japanese Patent Application Laid-Open (JP-A) No. 2002-67473
Patent Literature 5 Japanese Patent Application Laid-Open (JP-A) No. 2002-69346
Patent Literature 6 Japanese Patent Application Laid-Open (JP-A) No. 2002-301857
Patent Literature 7 Japanese Patent Application Laid-Open (JP-A) No. 6-171072
Patent Literature 8 Japanese Patent Application Laid-Open (JP-A) No. 2005-220352
Patent Literature 9 Japanese Patent Application Laid-Open (JP-A) No. 2003-201427
Patent Literature 10 Japanese Patent Application Laid-Open (JP-A) No. 07-292302
Patent Literature 11 Japanese Patent Application Laid-Open (JP-A) No. 05-230409
Patent Literature 12 Japanese Patent Application Laid-Open (JP-A) No. 04-018462